Bi--Ca--Sr--Cu--O based, Tl--Ca--Sr--Cu--O based, Tl--Ca--Ba--Cu--O based and Tl--Ca--Ba--Cu--O based superconducting ceramic materials (hereinafter, abbreviated as (Bi,Tl)--Ca--(Sr,Ba)--Cu--O based superconducting ceramic materials) have recently been proposed. It is well known that these ceramic materials are prepared by a process including the steps of providing starting powders, i.e., powders of Bi oxide (Bi.sub.2 O.sub.3), Tl oxide (Tl.sub.2 O.sub.3), Ca carbonate (CaCO.sub.3), Sr carbonate (SrCO.sub.3) or Ba carbonate (BaCO.sub.3), and Cu oxide (CuO), compounding and mixing them in a predetermined compounding ratio to obtain a mixed powder, subjecting the mixed powder repeatedly two or three times to calcining at a temperature of from 700.degree. to 800.degree. C. for a certain retention time and grinding to form a (Bi or Tl)--Ca--(Sr or Ba)--Cu--O based superconducting oxide powder, press-molding the superconducting oxide powder under ordinary conditions, and then sintering the powder.
However, the compositions of (Bi or Tl)--Ca--(Sr or Ba)--Cu--O based superconducting oxide powders prepared by the above--described conventional process tends to vary because volatile components, such as Bi and Tl, evaporate during calcination. This results in inadequate superconducting characteristics.
Also, when a carbonate powder, such as Ca carbonate, Sr carbonate, or Ba carbonate is used as starting powders, carbon remains even after repeated calcination of the powders. It is difficult to reduce the carbon content to 0.5% or less by weight by, for example, 5 repetitions of calcination and grinding. When such high-carbon-content (Bi or Tl)--Ca--(Sr or Ba)--Cu--O based superconducting oxide powder is used as a starting material for preparing superconducting ceramic materials, the carbon residue deposits at grain boundaries during calcination, giving inadequate superconducting characteristics.